Heat a sauté pan on medium heat. Once hot, add the oil. Saute the sausage and onion until the sausage is browned, then stir in the spinach until wilted. Remove from the heat.
Combine the eggs, cream, sausage mixture, cheese, and season with salt and pepper in a bowl.
Pour the mixture into the pie crust.
Bake until a toothpick inserted into the center comes out clean (about 25 to 30 minutes). Remove from the heat, and let stand for 5 minutes before cutting into wedges and serving warm.